Transition, radiationless theory

Deuterium substitution leads to a decrease in the non-radiative rate by several orders of magnitude. The application of radiationless transition theory indicates that the large isotope effect is due to a large decrease in Franck-Condon factors which more than overcomes an increased density of states. 

In 1976 TET was first applied to H abstractions [53]. One year later Suhnel [54] used TET to explain radiationless transitions in indigoid compounds, and Phillips [55] tested the harmonic approximation used by the theory in H abstractions. CT interactions [56] and substituent effects [57] in H abstractions were also addressed, as well as H abstractions by uranyl ion [58]. Support for TET also came from the demonstration [59] that in radiationless transitions theories, some Franck-Condon factors may be expressed by a nuclear tunneling formula like the TET one. 

The near identity of the geometry in the E and A2 states means that the weak coupling limit of radiationless transition theory, in which represents a tunnelling rate, is applicable [15]. In this theory three parameters are important, the E — A2 energy gap (A ), the energy of the high-frequency... 

The observation of novel quantum beats in the spectrally resolved fluorescence of anthracene21 forced one to consider, within the context of radiationless transition theory, the details of how IVR might be manifested in beat-modulated fluorescence decays. This work led to the concepts of phase-shifted quantum beats and restricted IVR,30a,4° and to a general set of results306 pertaining to the decays of spectrally resolved fluorescence in situations where an arbitrary number of vibrational levels, coupled by anharmonic coupling, participate in IVR. Moreover, three regimes of IVR have been identified no IVR, restricted (or coherent) IVR, and dissipative IVR.42... 

Figure 14. Temperature dependence of the relative luminescence intensity at 462 nm. I0 represents the luminescence intensity at 7.6 K. The solid curves represent theoretical fits based on multiphonon-induced radiationless transition theory. (Taken from reference 64 with permission.)...

A previous review provides a description of the theory of electronic relaxation in polyatomic molecules with particular emphasis on the vibronic state dependence of radiationless transition rates. A sequal review considers the general question of collisional effects on electronic relaxation, while the present one covers only the special phenomenon of collision-induced intersystem crossing. It departs from the other collisional effects review in presenting only a qualitative description of the theory the full theoretical details can be obtained from the previous review and the original papers.As a review of the basic concepts of radiationless transitions theory is necessary as a prelude to a discussion of collision-induced intersystem crossing, considerable overlap exists between this section and Section II of the previous collision effects review. However, since many concepts from radiationless transition theory, such as the nature and criteria for irreversible decay, the role of the preparation of the initial state, the occurrence of intramolecular vibrational relaxation, etc. pervade the other papers on laser chemistry in these volumes, it is useful to recall the primary results of the theory of electronic relaxation in isolated molecules and its relevance to the material in the present volume as well as to this review. 

Scholes GD and Ghiggino KP. Rate expressions for excitation transfer 1. Radiationless transition theory perspective. J. Chem. Phys. 1994b 101 1251-1261. 

X = 8000 cm" ). It is seen that the charge recombination process leading to the Cr(ni) doublet state is expected to be in the nearly activationless regime, whereas that leading to the ground state is likely to lie deep into the "inverted region" of electron transfer (section 1.3.2). In terms of radiationless transition theory, the excited-state charge recombination is favored by its... 

K. Maruszewski, K. Bajdor, D. P. Strommen and J. R. Kincaid, Position-dependent deuteration effects on the nonradiative decay of the 3MLCT state of tri (bipyridine)tuthenium (II). An e/qrerimental evaluation of radiationless transition theory, / Phys. Chem. 99,6286-6293 (1995). 

The Sj radiationless transition rate is sensitive to both solvatochromic and substituent-induced shifts of the Sj - Sj energy gap. Figure 1.2 shows that an almost linear dependence of the logarithm of the rate constant of radiationless decay on the Sj - Sj energy gap is observed for a series of 1-and 1,3-fluorine-substituted azulenes in a range of solvents, as expected if the energy gap law of radiationless transition theory applies and internal conversion is the sole Sj decay process. 1,3-Difluoroazulene in ethanol... 

Using the data obtained by Meyer and co-workers for the ligand-to-ligand charge-transfer absorption bands of the complex represented in Figure 15.18 gives = 45 cm (= 0.53 kJ morO- This value of the electronic coupling is within the limits required by radiationless transition theories. 

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